Degradable adhesive film and degradable resin composition

ABSTRACT

Articles which can be degraded and disappear in the natural environment are a degradable adhesive film which can be used for surface protection or indication after printing on the film surface and has an adhesive layer on one side of a substrate film obtained from a lactic acid base polymer such as polylactic acid and a lactic acid/hydroxycarboxylic acid copolymer having a molecular weight of 30,000-500,000, and a degradable resin composition which is excellent in weatherability and comprises 100 parts by weight of a lactic acid base polymer and 0.001-5 parts by weight of one or more additives selected from ultraviolet absorbers and light stabilizers.

BACKGROUND OF THE INVENTION AND RELATED ART

1. Field of the Invention

The present invention relates to a degradable adhesive film and adegradable resin composition. More particularly, the invention relatesto a degradable resin composition used for the substrate of a polylacticacid based degradable adhesive film for surface protection which is usedby being tentatively adhered on the surface of adherends including metalplates such as stainless steel and aluminum or their workpieces, resincoated woodboards, decorative laminates, wood and metal furniture andautomotive bodies, or by being provisionally adhered on the surface of asemiconductor wafer in the fabrication step; a polylactic acid baseddegradable adhesive film for display which is printed or coated on thesurface; a pressure-sensitive adhesive tape for vegetable tyingmaterials and stationery products; and other degradable adhesive filmsfor various uses.

2. Related Art of the Invention

Conventionally, adhesive films or tapes using films of polyvinylchloride, polyolefin or an ethylene/vinyl acetate copolymer as substrateand mounting an adhesive layer on the substrate surface have been widelyused as an adhesive film for surface protection which is used by beingtentatively adhered on the surface of adherends including metal platessuch as stainless steel and aluminum or their workpieces, resin coatedwoodboards, decorative laminates, wood and metal furniture, measuringinstruments such as watches, and automotive bodies; as an adhesive filmfor semiconductor wafer fabrication which is used for protection byadhering on the wafer surface having a built-in semiconductor IC in thestep of grinding or dicing the other surface (the back) of said wafer;and as an adhesive film for display which is printed or coated on thefilm surface.

For example, Japanese Laid-Open Patent HEI 2-107684 discloses asurface-protective film having an adhesive layer on one surface of aflexible vinyl chloride resin film comprising a high polymer plasticizerhaving a molecular weight of 500 or more. Japanese Laid-Open Patent SHO61-10242 (U.S. Pat. Nos. 4,853,286 and 4,928,438) discloses an adhesivefilm for wafer fabrication which has an adhesive layer on the surface ofsubstrate film such as an ethylene/vinyl acetate copolymer film orpolybutadiene film which has a Shore-D hardness of 40 or less.

Japanese Patent Laid-Open Publication HEI 2-300281 discloses an adhesivefilm for protection which is tentatively adhered on the surface of anautomotive body in order to prevent the surface from corrosion anddeterioration by rain, dust or sea breezes during transportation andstorage in the course of delivering new automotives (four- and two-wheeled painting-completed vehicles) to the customers. The adhesive filmfor automotive-protection is prepared by applying an adhesive to onesurface of a film of general purpose resin such as polyethylene,polypropylene, polyvinyl chloride and an ethylene/vinyl acetatecopolymer.

Conventionally, in the case of conducting a notice, advertisement orpropagation by illustrating a letter, drawing, stamp or mark on asignboard and wall or decorating a car body or building, it is widelyperformed to stick on the above adherends said general purpose resinfilm which is printed, transcripted or painted with the letter etc.

As a result of the object for use, the above various adhesive films forsurface protection are almost stripped and abandoned after protectingthe surface for a prescribed period by sticking to the adherends.However, the above general purpose resin used for the substrate of theseconventional adhesive films does not degrade or has a very slowdegradation rate under the natural environment. Consequently, thesefilms semipermanently remain when disposed after use by burying in soil,and impair the scenery or destruct the living environment of marineorganisms when abandoned in the ocean. Further, these films require alarge amount of energy for incineration and polyvinyl chloride films inparticular have problems of developing toxic gas. As a result, wastedisposal of these general purpose resin films has been a serious socialproblem.

A lactic acid base polymer has been already known as a hydrolyzablepolymer or a bioabsorbable polymer. For example, Japanese PatentPublication SHO 49-36597 discloses an auxiliary surgical tool obtainedfrom a lactic acid/glycolic acid copolymer consisting of 65˜85% byweight of lactic acid units and 35˜15% by weight of glycolic acid units.Japanese Patent Laid-Open Publication 62-501611 discloses a medicaltransplanting material obtained from a copolymer of caprolactone andlactide, a cyclic dimer of lactic acid.

Polylactic acid or a lactic acid/hydroxycarboxylic acid copolymer can beeffectively hydrolyzed by atmospheric moisture and thus has recentlybeen intended to apply to a fundamental component of degradable generalpurpose materials for disposable uses other than medical tools. Variousinformation has already been obtained on the hydrolysis rate ofpolylactic acid and a lactic acid/hydroxycarboxylic acid copolymer. Itis hence relatively easy to design materials so as to meet thedegradation period required for disposable uses. For example, highmolecular weight poly(L-lactic acid) is suited for a use period of about6 months, and a lactic acid/glycolic acid copolymer is suited for useswhere the use period is several days and quick decomposition is desiredafter use.

According to the knowledge of the inventors, however, outdoor use ofconventional materials prepared from lactic acid base polymers such aspolylactic acid and a lactic acid/hydroxycarboxylic acid copolymergenerally leads to distinctly faster reduction of strength as comparedwith indoor use or uses in a dark place or living body. It has beenfound that phenomena such as embrittlement, rupture and disappearanceoccur earlier than expected. For example a film which was expected tohold its strength for at least 6 months at ambient temperature in viewof information on the rate of hydrolysis was embrittled after outdooruse for about a month and could not perform its function any more.Further, the rate of acceleration of the decomposition could not beanticipated at all and the decomposition period was diversified.

As described above, earlier decomposition than prescribed degradationperiod sometimes results in a serious problem for utilizing a lacticacid based polymer such as polylactic acid and a lacticacid/hydroxycarboxylic acid copolymer as a degradable material. Suchproblem is a great disadvantage which cannot be overlooked at all.

SUMMARY OF THE INVENTION

The object of the invention is to provide a degradable adhesive film byusing a substrate film which can be degraded and disappeared in anatural environment after use.

Another object of the invention is to provide a degradable adhesive filmby using a substrate film which is excellent in weatherability and canbe degraded and disappeared in a natural environment after use.

A further object of the invention is to provide a degradable adhesivefilm for use in surface protection, display, tying and stationaryproducts by using a substrate film which can be degraded and disappearedin a natural environment after use.

A still further object of the invention is to provide a degradablemolding-resin composition which has inhibited decomposition andexcellent weatherability primarily in outdoor use.

That is, one aspect of the invention is a degradable adhesive filmhaving an adhesive layer on the surface of a substrate film primarilyconsisting of a lactic acid base polymer, a degradable adhesive filmhaving printing or a coating on the surface of a substrate filmprimarily consisting of a lactic acid base polymer and an adhesive layeron the other side of the substrate film, and a degradable resincomposition having an excellent weatherability due to the addition of aspecific amount of ultraviolet absorbers to a lactic acid base polymer.

The invention provides a degradable adhesive film having an adhesivelayer on the surface of substrate film obtained from a lactic acid basepolymer. The degradable adhesive film of the invention is prepared byforming a film with a lactic acid base polymer, coating an adhesive onone surface of the lactic acid base polymer film thus obtained, anddrying to form an adhesive layer.

The invention also provides a degradable adhesive display film having anadhesive layer on the surface of a substrate film comprised of a lacticacid base polymer and comprising a letter, drawing, stamp or mark whichis described by printing or painting said degradable film. Saiddegradable adhesive display film is prepared by printing or painting thesurface of a lactic acid base polymer film obtained by forming thelactic acid base polymer, successively coating an adhesive on the otherside of said films, and drying to form an adhesive layer.

The degradable adhesive film of the invention maintains a certainstrength for a prescribed period and is hydrolyzed in the naturalenvironment when abandoned after use. Thus, the film does not accumulateas waste matter. The film also has almost the same adhesive force asconventional adhesive films. Consequently, the film of the invention isuseful as a degradable adhesive film for surface protection which isused by being tentatively adhered on the surface of adherends includingmetal plates or work pieces thereof, resin coated woodboards, decorativelaminates, wood and metal furniture, measuring instruments such aswatches and automotive bodies; as a degradable adhesive film forsemiconductor wafer fabrication which is used for protection by adheringon the wafer surface having a built-in semiconductor IC in the step ofgrinding or dicing the other surface (the back) of said wafer; as adegradable adhesive display film which is printed and coated on the filmsurface; and as other pressure sensitive adhesive tapes for vegetabletying materials and stationery products.

Further, the invention provides a degradable resin compositioncomprising 100 parts by weight of a lactic acid base polymer and 0.001˜5parts by weight of one or more additives selected from ultravioletabsorbers and light stabilizers. Said degradable resin composition isprepared by mixing a lactic acid base polymer with a specific amount ofauxiliary agents such as ultraviolet absorbers.

The degradable adhesive film of the invention has a characteristic ofdegrading in the natural environment because a film obtained by forminga lactic acid base polymer is used for a substrate film. Consequently,the degradable adhesive film of the invention can be degraded with easewhen abandoned after use and does not accumulate as waste matters.Additionally, a lactic acid base polymer has active groups in thepolymer chain and the film prepared from the polymer is hence excellentin coating properties of adhesiveness, printability by ink, andapplication properties of coating. As a result, the degradable adhesivefilm of the invention has good adhesion between the substrate film andthe adhesive and can be printed or painted with ease on the surface.Further, no corona discharge treatment for enhancing the applicationproperties of the substrate film surface is required and preparationsteps of the adhesive film can be simplified.

The degradable resin composition of the invention is excellent inweatherability. Although the degradable product formed from the resincomposition is used outdoors, the product exhibits the same degradationbehavior as used indoors or in a dark place. The degradable product canmaintain essential mechanical properties of the lactic acid base polymerduring the use period and degrade after use on the basis of theessential hydrolytic properties, and is thus useful for a material ofthrowaway formed products which are mainly used outdoors.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will hereinafter be illustrated in detail.

The term "Lactic acid base polymer" in the invention means polylacticacid or a copolymer of lactic acid with a hydroxycarboxylic acid.

L- and D- Isomers are present in lactic acid. When referred to simply aslactic acid, the term means L-lactic acid, D-lactic acid or a mixture ofL- and D-lactic acid unless otherwise noted. A molecular weight of thepolymer means a weight average molecular weight unless otherwise noted.

Polylactic acid which can be used in the invention includes poly(L-lactic acid) having structural units composed of L-lactic acid alone,poly(D-lactic acid) having structural units composed of D-lactic acidalone, and poly(DL-lactic acid) having L-lactic acid units and D-lacticacid units in an arbitrary ratio.

The lactic acid/hydroxycarboxylic acid copolymer which can be used inthe invention is prepared from lactic acid including the above variouslactic acids and hydroxycarboxylic acids including glycolic acid,hydroxyacetic acid, hydroxyvaleric acid, hydroxycaproic acid andhydroxyheptanoic acid.

Polylactic acid and the lactic acid/hydroxycarboxylic acid copolymer ofthe invention can be prepared by dehydration polycondensation of lacticacid or lactic acid and hydroxycarboxylic acid. Direct dehydrationpolycondensation includes a process for carrying out hot dehydrationcondensation of lactic acid or lactic acid and other hydroxycarboxylicacids preferably in a solvent and additionally conducting the reactionwhile removing formed water out of the reaction system. The homopolymersand copolymers of lactic acid can also be prepared by ring openingpolymerization of lactide which is a cyclic dimer of lactic acid,glycolide which is a cyclic dimer of glycolic acid, and cyclic esterssuch as caprolactone, propiolactone, butyrolactone and valerolactone.

Formed products of a lactic acid base polymer are degraded in water orsoil after abandonment and are also hydrolyzed during use by atmosphericmoisture or water. Consequently, the molecular weight of the polymer inthe substrate film used is an important factor. Tensile strength of thefilm depends upon the molecular weight. Low-molecular weight decreasestensile strength and high molecular weight increases tensile strength.However, too high molecular weight lowers processability and makes filmforming difficult. Consequently, the molecular weight of the lactic acidbase polymer used in the invention is in the range of 10,000˜1,000,000,preferably 30,000˜500,000.

In the case of polylactic acid, a sheet or film formed by extrusion orcalendering sometimes can eliminate transparency due to progress ofcrystallization when these products are subjected to heat treatment suchas vacuum forming, pressure forming, vacuum/pressure forming and heatsetting. Polylactic acid having 100% by weight of L-lactic acid units orD-lactic acid units must be vacuum formed or pressure formed atrelatively low temperatures such as 60°˜90° C. in order to obtaintransparent products. Such a narrow range of processing temperature is adisadvantage. Consequently, poly(DL-lactic acid) comprising L-lacticacid units and D-lactic acids units is preferred for preparingtransparent products rather than poly(L-lactic acid) consisting ofL-lactic acid units alone or poly(D-lactic acid) consisting of D-lacticacid alone. The composition of polylactic acid which can be preferablyused is poly(L-lactic acid) or poly(DL-lactic acid) which comprises50˜100% by mole, preferably 70˜100% by mole of L-lactic acid andpoly(D-lactic acid) or poly(DL-lactic acid) which comprises 50˜100% bymole, preferably 70˜100% by mole of D-lactic acid.

In the case of a lactic acid/hydroxycarboxylic acid copolymer,degradability depends upon the content of lactic acid. A low content oflactic acid often leads to very slow or insufficient degradation whenabandoned after use. Consequently, the content of lactic acid units ispreferably 10% by mole or more.

Practically, a preferred composition of the lactic acid/glycolic acidcopolymer comprises 30-98% by mole of lactic acid units and 70˜2% bymole of glycolic acid units. A more preferred composition comprises70-98% by mole of lactic acid units and 30-2% by mole of glycolic acidunits. A preferred composition of the lactic acid/hydroxycaproic acidcopolymer comprises 10˜98% by mole of lactic acid units and 90˜2% bymole of hydroxycaproic acid units. A more preferred compositioncomprises 20˜98% by mole of lactic acid units and 80˜2% by mole ofhydroxycaproic acid units.

The most suitable molecular weight and copolymer composition of thelactic acid base polymer used in the invention is arbitrarily selectedfrom the above range so as to meet the longest adhesion time inrespective use.

According to the knowledge of the present inventors, poly(L-lactic acid)having a molecular weight of 150,000 or more can be applied to ause-life of 6 months or more. Poly(L-lactic acid) having a molecularweight of 50,000 or more or poly(DL-lactic acid) having a molecularweight of 100,000 or more and comprising less than 5% by mole ofD-lactic acid can be applied to a use-life of about a month.

The above polymers and additionally poly(DL-lactic acid) comprising lessthan 25% by mole of D-lactic acid units and a lactic acid/glycolic acidcopolymer comprising less than 15% by mole of glycolic acid units can beapplied to a use-life of from several days to a few weeks. Further,formed products which require high flexibility can be prepared, forexample, from a lactic acid/hydroxycaproic acid copolymer comprisingabout 60% mole of hydroxycaproic acid units. In the case, the use-lifeof the formed product is about 3 months.

In the case of preparing a lactic acid base polymer by directdehydrating polycondensation of lactic acid and hydroxycarboxylic acid,dehydrating condensation of L-lactic acid, D-lactic acid or a mixture ofthese acids, or dehydrating condensation of L-lactic acid, D-lactic acidor a mixture of these acids and hydroxycarboxylic acid is carried out ina reaction mixture containing an organic solvent preferably andsubstantially in the absence of water. Any of L-lactic acid, D-lacticacid and a mixture of these acids can be used for the raw material ofthe lactic acid base polymer.

The degradable resin composition of the invention can be obtained bymixing 100 parts by weight of a lactic acid base polymer with 0.001˜5parts by weight, preferably 0.05˜5 parts by weight of one or moreadditives selected from ultraviolet absorbers and light stabilizers.

When the amount of the ultraviolet absorbers and light stabilizers issmall, weatherability in outdoor use of the formed product becomes poor,that is, acceleration of degradation by exposure to ultraviolet rayscannot be sufficiently inhibited. On the other hand, too great an amountof these additives gives adverse effects on the essential properties ofthe lactic acid base polymer. Consequently, the amount of theseadditives is preferably in the above range.

Exemplary ultraviolet absorbers and light stabilizers which can be usedin the invention include phenyl salicylate, p-tert-butylphenylsalicylate and other salicylate derivatives; 2,4-dihydroxybenzophenone,2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone,2,2'-dihydroxy-4,4'-dimethoxybenzophenone,2-hydroxy-4-methoxy-2'-carboxybenzophenone,2-hydroxy-4-n-octoxy-benzophenone, 2,2',4,4'-tetrahydroxybenzophenone,4-dodecyloxy-2-hydroxybenzophenone,bis(5-benzoyl-4-hydroxy-2-methoxyphenyl)methane and other benzophenones;2(2'-hydroxy-5'-methylphenyl)benzotriazole,2-(2'-hydroxy-3',5'-di-tert-2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole,2-(2'-hydroxy-3',5'-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2'-hydroxy-5'-tert-octylphenyl)benzotriazole,2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole,2-[2'-hydroxy-3'-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'-methylphenyl]benzotriazole,2,2'-methylenebis[4-(1,1,3,3-tetramethylbutyl)-tetramethylbutyl-6-(2H-benzotriazole-2-yl)phenoland other benzotriazoles; oxalic anilide derivatives known as SanduvorEPU (Trade Mark) and Sanduvor VSU (Trade Mark),2-ethoxy-5-tert-butyl-2'-ethyloxalic bisanilide, 2-ethoxy-2-ethyloxalicbisanilide, 2,4 -di-tert-butylphenyl3,5-di-tert-butyl-4-hydroxybenzoate, 2-ethylhexyl2-cyano-3,3-diphenylacrylate,1,3-bis(4-benzoyl-3-hydroxyphenoxy)-2-propyl acrylate,1,3-bis(4-benzoyl-3-hydroxyphenoxy)-2-propyl methacrylate,2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, methylo-benzoylbenzoate, ethyl 2-cyano-3,3diphenylacrylate,2-hydroxy-4-benzyloxybenzophenone, nickel dibutyldithiocarbamate, nickelthiobisphenol complex, nickel containing organic stabilizers, inorganicand organic complexes containing barium, sodium and phosphorus,semicarbazone based light stabilizers, zinc oxide based ultravioletstabilizers and synergistic agents known as Sanshade (Trade Mark),bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, 1-[2-{3-(3,5-di-tert-butyl-4-hydroxy-phenyl)propionyloxy} ethyl]-4-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-2,2,6,6-tetramethylpiperidine,8-benzyl-7,7,9,9-tetramethyl-3-octyl-1,2,3-triazaspiro[4,5]undecane-2,4-dione,4-benzoyloxy-2,2,6,6-tetramethylpiperidine, dimethylsuccinate/1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidinepolycondensate,poly[6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl][2,2,6,6-tetramethyl-4-piperidyl)-imino]hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino],2-(3,5-di-tert-butyl-4-hydroxybenzyl)-2-n-butylmalonicbis(1,2,2,6,6-pentamethyl-4-piperidyl),tetrakis(2,2,6,6-tetramethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate, condensate of1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinoland tridecyl alcohol, condensate of 1,2,3,4-butanetetracarboxylic acid,2,2,6,6-tetramethyl-4-piperidinol and tridecyl alcohol, condensate of1,2,3,4-butanetetracarboxylic acid, 1,2,2,6,6-pentamethyl-4-piperidinoland β, β, β', β', -tetramethyl-3,9-(2,4,8,10-tetraoxaspiro[5,5]undecane) diethanol, condensate of 1,2,3,4-butanetetracarboxylicacid, 2,2,6,6-tetramethyl-4-piperidinol and β, β, β',β',-tetramethyl-3,9-(2,4,8,10-tetraoxaspiro [5,5]undecane) diethanol,1,2,2,6,6-pentamethyl-4-piperidyl methacrylate,2,2,6,6-tetramethyl-4-piperidyl methacrylate and other hindered amines.

Additionally, [2,2'-thiobis-(4-tert-octylphenolite)3-n-butylamine nickeland [2,2'-thiobis-(4-tert-octylphenolite)]2-ethylhexylamine nickel areunsuitable for the degradable polymer of the invention because thesecompounds sometimes lead to decomposition of polylactic acid and alactic acid/hydroxycarboxylic acid copolymer in the mixing step.

Methods for preparing a degradable resin composition by mixing a lacticacid base polymer with ultraviolet absorbers and/or light stabilizersinclude a method for adding a prescribed amount of ultraviolet absorbersand/or light absorbers to the lactic acid base polymer and mixing with amixer such as a ribbon blender and Henschel mixer in the vicinity ofroom temperature, a method for melting the lactic acid base polymer byheating to 100°˜280° C. and kneading with a prescribed amount ofultraviolet absorbers and/or light stabilizers, and a method fordissolving the lactic acid base polymer and ultraviolet absorbers and/orlight absorbers in solvents such as chloroform, methylene chloride,benzene, toluene, xylene, dimethyl formamide, dimethyl sulfoxide anddimethyl imidazolidinone and mixing the solutions thus obtained.

The degradable resin composition of the invention can be mixed with aplasticizer, antioxidant, heat stabilizer, lubricant, pigment and otheradditives, if desired, in addition to the above ultraviolet absorbersand light stabilizers.

Plasticizers which can be used include, for example, di-n-octylphthalate, di-2-ethylhexyl phthalate, dibenzyl phthalate, diisodecylphthalate, ditridecyl phthalate, diundecyl phthalate, diisooctylphthalate and other phthalate derivatives; di-n-butyl adipate, dioctyladipate and other adipate derivatives; di-n-butyl maleate and othermaleate derivatives; tri-n-butyl citrate and other citrate derivatives;monobutyl itaconate and other itaconate derivatives; butyl oleate andother oleate derivatives; glycerol monoricinoleate and other ricinoleatederivatives; tricresyl phosphate, trixylenyl phosphate and otherphosphate esters; and other low molecular weight plasticizers and highmolecular weight plasticizers such as polyethylene adipate andpolyacrylate.

In the above plasticizers, preferred plasticizers include glyceroltriacetate (triacetine), lactic acid, lactide and lactic acid oligomershaving a polymerization degree of 2˜10.

The amount of a plasticizer which is added to the degradable resincomposition is optionally selected depending upon the flexibilityrequired for the formed product. Too much amount of addition leads tounfavorable bleeding out on the surface of the formed product.Consequently, the amount of the plasticizer is preferably in the rangeof 1˜50, parts by weight, more preferably 5˜20 parts by weight for 100parts by weight of the lactic acid base polymer.

The lactic acid base polymer comprising the plasticizer is preferred tohave low crystallinity in view of plasticizing efficiency and inhibitionof bleeding out. Consequently, poly(D, L-lactic acid) or a lacticacid/hydroxycarboxylic acid copolymer is preferably used in the case ofadding the plasticizer to the degradable resin composition.

The lactic acid base polymers which are more preferably used in thepresence of the plasticizer are poly(D,L-lactic acid) comprised of50˜98% by mole of L-lactic acid and 50˜2% by mole of D-lactic acid,poly(DL-lactic acid) comprised of 50˜98% by mole of D-lactic acid and50˜2% by mole of L-lactic acid, a lactic acid/glycolic acid copolymercomprised of 98˜30% by mole of lactic acid units and 2˜70% by mole ofglycolic acid units and a lactic acid/hydroxycaproic acid copolymercomprised of 08˜10% by mole of lactic acid units and 2/90% mole ofhydroxycaproic acid units.

These polymers are effectively plasticized with the plasticizer and caninhibit bleeding of the plasticizer.

Next, the degradable adhesive film of the invention will be explained.

The degradable adhesive film of the invention can be obtained by forminga substrate film from the above lactic acid base polymer through a knownfilm-forming process, for example, solution-casting process,melt-extrusion process and calendering process, and by mounting anadhesive layer on one surface of the substrate film.

The degradable adhesive film is often used outdoors and thus andultraviolet absorber and/or light stabilizer is preferably added to thesubstrate film. A very flexible substrate film containing theplasticizer is preferred depending upon uses. The antioxidant, heatstabilizer, lubricant, pigment and other additives can also be added.

Preparation of the substrate film by solution casting process is carriedout by dissolving in solvents such as chloroform, methylene chloride,benzene, acetonitrile, toluene, xylene, dimethyl formamide, dimethylsulfoxide and dimethyl imidozolidinone, casting the solution obtained ona flat surface, and removing the solvent from the solution.

In the melt-extrusion process, too low a kneading temperature leads tounstable extrusion and is liable to cause an overload. On the otherhand, too high an extrusion temperature results in violent decompositionof the lactic acid base polymer and unfavorably generates molecularweight reduction, lowering of strength and discoloration. Consequently,the kneading temperature is in the range of preferably 100°˜280° C.,more preferably 130°˜250° C. The extrusion die has a circular or linearslit and is in a temperature range almost the same as maintained inkneading.

Stretching after forming the film is not always necessary. If stretchingis desired, the film is at least monoaxially stretched 1.1˜10 times,preferably 2˜7 times. Stretching temperature is selected from the rangeof 60°˜210° C. depending upon the kind of the lactic acid base polymerused. Biaxial stretching is preferred in view of strength of theresulting film.

Thickness of the film is in the range of 10˜2000μm, preferably 20˜500μm, more preferably 100˜300 μm and suitable selected depending uponuses.

Mounting of the adhesive layer on the side of the film thus obtained ispreferably carried out by coating the adhesive on the surface of thesubstrate film. Exemplary coating method includes conventionally knownmethods, for example, roll coating, dipping, brushing and spraying.These methods can spread the adhesive on the whole surface or a portionof the substrate film. Thickness of the adhesive layer is suitablydetermined depending upon the shape surface conditions and use of theadherend and generally has a preferred range of 2˜200 μm.

After coating the adhesive, the substrate film is dried in an oven. Thedrying temperature differs depending upon the thickness of the substratefilm, composition of the adhesive layer and is preferably 40°˜180° C.more preferably 60°-120° C. A drying temperature lower than 40° C.cannot perform sufficient drying. On the other hand, a dryingtemperature exceeding 180° C. leads to shrinkage of the substrate filmand unfavorably develops defects such as wrinkling.

Drying time differs depending upon the composition and thickness of thesubstrate film, kind of the adhesive and thickness of adhesive layer. Itis usually preferred to continuously transfer through a drying oven at arate of 2˜100 m/min and have a residence time of 0.1˜30 minutes in thedrying oven.

Alternatively, a process which can be employed is to coat the adhesiveby the above method on one side of a film such as a polypropylene filmwhich has good releasability, dry the coated film to form an adhesivelayer, successively laminate a substrate film, i.e. a lactic acid basepolymer film on the surface of said adhesive layer and press thelaminate to transfer the adhesive layer onto the substrate film.

The adhesive to be coated on one side of the substrate film includes forexample, rubber base adhesives primarily comprising natural rubber andsynthetic rubber, and synthetic resin based adhesives primarilycomprising acrylic resin, silicone resin, urethane resin, epoxy resin,melamine resin, phenolic resin and vinyl acetate resin. Acrylic resinbased adhesives are excellent in weatherability and particularlysuitable for outdoor uses.

Exemplary acrylic resin based adhesives include copolymers obtained bycopolymerizing primary components such as ethyl acrylate, butyl acrylateand 2-ethylhexyl acrylate with other vinyl monomers. The adhesives areexemplified by a solution based adhesive containing a uniform solutionof said copolymer in an organic solvent and an aqueous emulsion basedadhesive containing fine particles dispersed in water.

Particularly preferred adhesives are obtained by emulsioncopolymerization of a monomer mixture containing an acrylic acid alkylester monomer and a monomer having carboxyl groups. If desired, moreparticularly preferred adhesives are obtained by emulsioncopolymerization of a monomer mixture containing a vinyl monomer,polyfunctional monomer and internally crosslinkable monomer which arecapable of copolymerizing with these monomers.

Acrylic acid alkyl ester monomers include, for example, methyl acrylate,methyl metharylate, ethyl acrylate, ethyl methacrylate, propyl acrylate,propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate,hexyl methacrylate, octyl acrylate, octyl methacrylate, nonyl acrylate,nonyl methacrylate, dodecyl acrylate and dodecyl methacrylate. The alkylgroups in the ester monomer can be straight or branched. The acrylicacid alkyl ester monomers can be used singly or as a mixture dependingupon the object.

Monomers having carboxyl groups include, for example acrylic acid,methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaricacid. These monomers are preferably copolymerized in an amount of 0.1˜10parts by weight for 100 parts by weight of the monomers which constitutethe acrylic resin based emulsion adhesive. The carboxyl groups in theadhesive react with the below described crosslinking agents to form acrosslinked structure. Thus, too small an amount of the monomers havingcarboxyl groups in the adhesive cannot form a satisfactory crosslinkedstructure, leads to shortage of cohesive force and is liable to transferthe adhesive onto the adherend. On the other hand, too large an amountof the monomers having carboxyl groups unfavorably makes the emulsionpolymerization system unstable. Thus, the above range of amount ispreferred.

Vinyl monomers which can copolymerize with acrylic acid alkyl estermonomer and the monomer having carboxyl groups include, for example,hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropylacrylate, hydroxypropyl methacrylate, acrylamide, methacrylamide,dimethylaminoacrylate, dimethylaminomethacrylate, vinyl acetate, styreneand acrylonitrile.

Crosslinking agent, surface active agents and organic solvent can alsobe added to the adhesive, when desired. Preferred surface active agentsare nonionic surfactants in order to prevent contamination and corrosionof the adherend. The amount of the agents is 0.01˜50 parts by weight,preferably 0.1˜10 parts by weight for 100 parts by weight of theadhesive. Addition of the surface active agents improves coatingproperties and is effective for inhibiting time-dependent viscosityincrease of the adhesive sticking to the adherend.

Exemplary crosslinking agents include sorbitol polyglycidyl ether,polyglycol polyglycidyl ether, pentaerythritol polyglycidyl ether,trimethylolpropane polyglycidyl ether and other epoxy based resins;methylol melamine, melamine alkyl ether, melamine urea condensate,methylol alkyl ether containing urea-formaldehyde precondensate,guanamine resin and other melamine based resins;1,1'-(methylene-di-p-phenylene)bis-3,3'-aziridinylurea,1,1'-(hexamethylene)bis-3,3'-aziridinylurea,ethylenebis(2-aziridinylpropionate), tris(1-aziridinyl) phosphine oxide,2,4,6-triaziridinyl-1,3,5-triazine,trimethylolpropanetris-(2-aziridinylpropionate) and other aziridinebased resins.

The crosslinking agent is added to the above acrylic base resin asintact when the agent is soluble in water or as a solution in an organicsolvent such as alcohol and acetone when the agent is insoluble inwater. Accelerator such as organic tin compounds, organic leadcompounds, organic cobalt compounds and amines can also be added inorder to accelerate the crosslinking reaction. The amount ofcrosslinking agent differs depending upon the kind of crosslinkingagents and adhesives and is preferably 0.01˜20 parts by weight for 100parts by weight of the adhesive. An amount of less than 0.01 parts byweight cannot sufficiently progress the crosslinking reaction. It is notrequired to add crosslinking agents exceeding 20 parts by weight in viewof numbers of functional groups which participate in the crosslinkingreaction in the adhesive layer.

Molecular weight of the adhesive is increased by addition of thecrosslinking agents and thus time-dependent viscosity increase in theadhesive after sticking to the adherend, and can also prevent theadhesive from transfer to the adherend when the adhesive film isreleased from the adherend.

The degradable adhesive film of the invention which has been attached tothe adherend for a prescribed period can be physically or mechanicallyreleased from the adherend and can also be removed by decompositionusing acid or alkali. Preferred acid includes hydrochloric acid andsulfuric acid. Preferred alkali includes sodium hydroxide and potassiumhydroxide. An aqueous sodium hydroxide solution is particularlypreferred. The adhesive film can also be heated in order to acceleratedecomposition and removal. For example, the substrate film can be almostcompletely removed by treating at 60° C. for about an hour in a 1Naqueous sodium hydroxide solution.

The degradable adhesion film of the invention can be used as surfaceprotection in the transportation and storage of metal plates such asstainless steel and aluminum or their workpiece, synthetic resin plates,synthetic resin molded articles, resin coated woodboards, decorativelaminates, wood and metal furniture, and instruments such as watches.

The degradable adhesive film of the invention can be used for corrosionprevention in place of protective coating in order to preventautomobiles from corrosion during transportation and storage,particularly from corrosion by sea breezes in marine transportation.Both protective coating for transportation and storage and removingoperation of the protective coating by use of a solvent becomeunnecessary by using the degradable adhesive film of the invention.

The degradable adhesive film of the invention can also be used forprotecting a semiconductor wafer from rupture in the step of grinding ordicing the back. That is, IC is mounted on one side of the semiconductorwafer, the adhesive film of the invention is attached onto the side (thesurface) having the built-in semiconductor circuit, and successively theother side (the back) of said semiconductor wafer is subjected togrinding and dicing. Stress developed by grinding and dicing can beabsorbed by the degradable adhesive film and the rupture of thesemiconductor wafer can thus be prevented.

In addition to the above uses, the degradable adhesive film of theinvention is cut into a width of 5˜50 mm and can be used as a degradablepressure-sensitive adhesive tape for stationery products and for tyingvegetables such as spinach and spring onions.

Further, the degradable adhesive display film can be obtained byprinting or painting one side of a film prepared from the lactic acidbase polymer through the above method and successively mounting aadhesive layer on the other side of the film. Printing or painting canbe applied to the surface where a adhesive layer is mounted, the surfacewhere the adhesive layer is not mounted, or both of these surfaces.

Practical examples of printing and painting include letter, drawing,design, stamp and mark for indication, notification, advertisement andpropagation. These printings and paintings can be manually drawn ormechanically printed. The degradable adhesive decoration film can beprepared by coating various colors of paint to the whole surface inplace of the letter and drawing or by drawing a pattern.

The degradable adhesive display film which was printed or painted asabove is adhered on a signboard or a building wall by way of theadhesive layer to carry out notification, indication, advertisement andpropagation. Such method can eliminate operation for directly paintingthe signboard or building wall and can efficiently perform indicationwith ease in many places. Circumstances are also the same in the case ofdecorating car bodies and buildings.

Printing and painting can be carried out by using a coating compound,dye, ink, pigment, Japanese ink, and other known colorants. Colorantswhich can be used include, for example, offset printing ink, rotogravureink (for polyethylene terephthalate, polyvinyl chloride andpolystyrene), Japanese ink, paint, UV ink, heat set ink and cinnabarseal ink.

In the above inks and paints, oil inks and oil paints obtained by usinga solvent such as chloroform, methylene chloride, benzene, toluene,xylene, dimethylformamide, dimethyl sulfoxide anddimethylimidazolidinone are unfavorable for use in the invention becausethese solvents dissolve the lactic acid base polymer.

The lactic acid base polymer film used in the invention comprises as aprimary component a lactic acid base polymer having ester groups in themolecular structure and is excellent in coating properties of theadhesive and coating compound and printing properties of inks.Consequently, it is not required to carry out post treatment, forexample, corona discharge treatment which is usually carried out forimproving coating properties of the adhesive and coating compound in thecase of a polyolefin base film, ethylene/vinyl acetate copolymer filmand polybutadiene film.

EXAMPLES

The present invention will hereinafter be illustrated in detail by wayof examples and comparative examples.

Preparation Examples 1˜9

[Preparation of a lactic acid base polymer by ring-openingpolymerization]

Marketed L-lactide (hereinafter referred to as L-LTD), DL-lactide(D-isomer 50 motes/L-isomer 50 moles, hereinafter referred to as DL-LTD)and glycolide (hereinafter referred to as GLD) were purified byrecrystallizing 4 times from ethyl acetate, respectively. Marketedε-caprolactone (hereinafter referred to as CL) was purified by drying oncalcium hydride and distillation.

To a glass reaction vessel having a silane treated internal surface, theabove L-LTD, DL-LTD, GLD, CL and a stannous octoate catalyst and alauryl alcohol molecular weight control let were charged in amountsillustrated in Table 1 and Table 2. Lauryl alcohol was used inPreparation Examples 1 and 2. The mixture obtained was dried overnightunder reduced pressure.

The reaction vessel was sealed under reduced pressure and the mixturewas heated to the temperature illustrated in Table 1 and Table 2 andpolymerized for a prescribed time. After finishing the reaction, thereaction mixture was dissolved in 20 times by weight of chloroform. Thechloroform solution was poured into hexane having 5 times by weight ofchloroform. Precipitated polymer was filtered and dried to obtain lacticacid base polymers P-1˜P-9.

Molecular weight of the lactic acid base polymers thus obtained wasmeasured by gel permeation chromatography (GPC) using chloroform as asolvent and calculated on the basis of reference polystyrene.Polymerization conditions and results of molecular weight measurement onthese lactic acid base polymers obtained are illustrated in Table 1 andTable 2.

Preparation Examples 10˜13

[Preparation of a lactic acid base polymer by direct dehydrationpolycondensation]

To a reaction vessel equipped with a Dean Stark trap, marketed 90%L-lactic acid (hereinafter referred to as LA), 90% D-lactic acid(hereinafter referred to as DA), glycolic acid (hereinafter referred toas GA) and hydroxycaproic acid (hereinafter referred to as HCA) werecharged in amounts illustrated in Table 3, respectively. The mixture washeated with stirring at 150° C. for 3 hours under 50 mmHg whiledistilling off water. Successively 6.2 g of tin powder was added and themixture was further stirred at 150° C. for 2 hours under 30 mmHg toobtain an oligomer. To the oligomer, 28.8 g of tin powder and 21.1 kg ofdiphenyl ether were added and an azeotropic dehydration reaction wascarried out at 150° C. under 35 mmHg. Distilled water was separated fromthe solvent in a water separator and the solvent alone was returned tothe reaction vessel. After 2 hours, the solvent which returned to thereaction vessel was changed to pass through a column packed with 4.6 kgof molecular sieve 3A before entering into the reaction vessel. Thereaction was further continued for 40 hrs at 150° C. under 35 mmHg toobtain a polylactic acid solution.

The solution was diluted by adding 44 kg of diphenyl ether and cooled to40 ° C. Precipitated powder was filtered, washed three times with 10 kgof n-hexane and dried at 60° C. under 50 mmHg. To the powder, 12.0 kg of0.5N aqueous hydrochloric acid solution and 12.0 kg of ethanol wereadded, stirred at 35° C. for an hour, filtered and dried at 60° C. under50 mmHg to obtain lactic acid base polymers P-10˜P-13 in the form ofpowder. The yield was about 85%.

P-10˜P-13 thus obtained were dissolved in chloroform and molecularweights were measured by GPC (polystyrene converted). Similarly, P-10was dissolved in acetonitrile and measured by high performance liquidchromatography (HLC). Residual monomer content in the polymer was 0.2%by weight. Polymerization conditions and molecular weights of the lacticacid base polymers thus obtained are illustrated in Table 3.

Preparation Example 14 [Preparation of Plasticizer]

To 1.8 kg of L-lactide in a reaction vessel, 1.0 kg of an aqueous lacticacid solution having a concentration of 87% by weight was added andheated at 100° C. for 2 hours. After cooling the reaction mixture toroom temperature, a transparent and viscous liquid was obtained. Theoligomer thus obtained was dissolved in chloroform and molecular weightdistribution was measured by GPC. Lactic acid and lactic acid oligomerwas contained in the liquid reaction product. The average polymerizationdegree was 2.8. The product will hereinafter be referred to asLA-oligomer.

                                      TABLE 1                                     __________________________________________________________________________              Preparation                                                                         Preparation                                                                         Preparation                                                                         Preparation                                                                         Preparation                                           Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 4                                                                           Example 5                                   __________________________________________________________________________    Lactic acid base                                                                        P-1   P-2   P-3   P-4   P-5                                         polymer                                                                       L -LTD (wt part)                                                                        100   100   90    --    --                                          DL-LTD (wt part)                                                                        --    --    10    80    40                                          GLD (wt part)                                                                           --    --    --    20    --                                          CL (wt part)                                                                            --    --    --    --    60                                          Catalyst (wt %)                                                                         0.010 0.015 0.030 0.015 0.015                                       Molecular weight                                                                        0.15  0.30  --    --    --                                          controller (wt %)                                                             Polymerization                                                                          180   180   120   120   120                                         temperature (°C.)                                                      Polymerization                                                                          4     4     60    60    60                                          time (hr)                                                                     Molecular 152   88    427   165   99                                          weight (x 1000)                                                               __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                               Preparation                                                                           Preparation                                                                             Preparation                                                                             Preparation                                       Example 6                                                                             Example 7 Example 8 Example 9                                  ______________________________________                                        Lactic acid                                                                            P-6       P-7       P-8     P-9                                      base polymer                                                                  L -LTD (wt                                                                             100       70        75      50                                       part)                                                                         DL-LTD (wt                                                                             --        30        20      50                                       part)                                                                         GLD (wt  --        --        5       --                                       part)                                                                         Catalyst 0.015     0.015     0.015   0.015                                    (wt %)                                                                        Polymeriza-                                                                            110       120       120     120                                      tion temper-                                                                  ature (°C.)                                                            Polymeriza-                                                                            160       120       120     120                                      tion time (hr)                                                                Molecular                                                                              376       410       280     354                                      weight                                                                        (x 1000)                                                                      ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                               Preparation                                                                           Preparation                                                                             Preparation                                                                             Preparation                                       Example 10                                                                            Example 11                                                                              Example 12                                                                              Example 13                                 ______________________________________                                        Lactic acid                                                                            P-10      P-11      P-12    P-13                                     base polymer                                                                  LA (kg)  8.5       9.0       10.0    5.0                                      DA (kg)  1.5       --        --      --                                       GA (kg)  --        1.0       --      --                                       CA (kg)  --        --        --      5.0                                      Oligomerization                                                               Tempera- 150       150       150     150                                      ture (°C.)                                                             Pressure 30        30        30      30                                       (mmHg)                                                                        Time (hr)                                                                              2         2         2       2                                        Polymerization                                                                Tempera- 150       150       150     150                                      ture (°C.)                                                             Pressure 35        35        35      35                                       (mmHg)                                                                        Time (hr)                                                                              42        42        12      42                                       Molecular                                                                              110       110       36      70                                       weight                                                                        (x 1000)                                                                      ______________________________________                                    

Examples 1˜7 and Comparative Example 1˜10

P-1, P-4 and P-5 which were obtained in the preparation examples wereindividually dissolved in chloroform in a concentration of 10% byweight. To the solution, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole(hereinafter referred to as TP), 2-hydroxy-4-n-octoxybenzophenone(hereinafter referred to as HOB) or 4-dodecyloxy-2-hydroxybenzophenone(hereinafter referred to as DHB) were individually added in a prescribedamount illustrated in Table 4, Table 7 or Table 8. The mixture wasthoroughly mixed and the resulting solution was cast on a glass plateand dried in the air. Successively, the solvent was completely removedby drying under reduced pressure to obtain a transparent film having athickness of 100 μm.

P-2 and P-3 which were obtained in the preparation examples weremelt-kneaded at 220° C. in a Brabender Plastograph.Bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (hereinafter referred to asHAL), TP or 2-(2'-hydroxy-3', 5'-di-tert-butylphenyl)benzotriazole(hereinafter referred to as T-320) was respectively added in aprescribed amount illustrated in Table 5 and Table 6 while melt-kneadingP-2 or P-3. Polymer compositions thus obtained were hot-pressed at thetemperature illustrated in Table 5 and Table 6 under pressure of 50kg/cm² to obtain transparent films having a thickness of 0.5 mm.

In Examples 1˜3 and Comparative Example 1, the film was allowed to standoutdoors by fixing at a place in the sun (the condition will hereinafterbe simply referred to as outdoors). In Comparative Example 2, the filmwas allowed to stand outdoors in a covered box so as to prevent exposurefrom direct rays of the sun and exposed to rain (the condition willhereinafter the simply referred to as dark). A portion of the film wascut on the 24th day and the 44th day. Molecular weight of the cut piecewas measured by GPC. Decomposition was distinctly inhibited in polymercompositions with addition of TP (Examples 1˜3) as compared with acomposition which was allowed stand outdoors without addition of TP.Particularly, Examples 2 and 3 exhibited almost the same level ofdecomposition as in the dark (Comparative Example 2). Results areillustrated in Table 4.

                                      TABLE 4                                     __________________________________________________________________________                                  Comparative                                                                          Comparative                                          Example 1                                                                           Example 2                                                                           Example 3                                                                           Example 1                                                                            Example 2                                __________________________________________________________________________    Lactic acid base                                                                          P-1   P-1   P-1   P-1    P-1                                      polymer                                                                       Ultraviolet                                                                         Compound                                                                            TP    TP    TP    --     --                                       absorber                                                                            wt %  0.005 0.1   5.0   0      0                                        or                                                                            light                                                                         stabilizer                                                                    Place       out door                                                                            out door                                                                            out door                                                                            out door                                                                             dark                                     Molecular                                                                            0 day                                                                              152000                                                                              152000                                                                              152000                                                                              152000 152000                                   weight                                                                               27 days                                                                            109000                                                                              139000                                                                              149000                                                                               43000 133000                                         197 days                                                                             36000                                                                              108000                                                                              129000                                                                              *1     106000                                   __________________________________________________________________________     Note                                                                          *1: Sampling was impossible by marked degradation                        

In Example 4 and Comparative Example 3, the films were allowed to standoutdoors as in Example 1. In Comparative Example 4, the film was allowedto stand in the dark as in Comparative Example 2. Tensile strength wasmeasured on the films after passing prescribed days. Results areillustrated in Table 5.

                  TABLE 5                                                         ______________________________________                                                             Compar-                                                                       ative Ex-                                                                              Comparative                                                 Example 4                                                                              ample 3  Example 4                                       ______________________________________                                        Lactic acid base polymer                                                                    P-2        P-2      P-2                                         Ultraviolet                                                                           Compound  HAL + TP   --     --                                        absorber                                                                              wt %      0.5 + 0.5   0      0                                        or                                                                            light                                                                         stabilizer                                                                    Press temperature (°C.)                                                              210        210      210                                         Place             out door   out door                                                                             dark                                      Molecular                                                                             0 day     68         66     66                                        weight  3 months  65         49     63                                                6 months  61         13     60                                        ______________________________________                                    

In Example 5 and Comparative Example 5, the films were allowed to standoutdoors. In Comparative Example 6, the film was allowed to stand in thedark. Tensile strength was measured on the films after passingprescribed days. Results are illustrated in Table 6.

                  TABLE 6                                                         ______________________________________                                                    Example                                                                              Comparative                                                                              Comparative                                                 5      Example 5  Example 6                                       ______________________________________                                        Lactic acid base polymer                                                                    P-3      P-3        P-3                                         Ultraviolet                                                                           Compound  T 320    --       --                                        absorber                                                                              wt %      2.0       0        0                                        or                                                                            light                                                                         stabilizer                                                                    Press temperature (°C.)                                                              190      190        190                                         Place             out door out door dark                                      Molecular                                                                             0 day     61       63       63                                        weight  3 months  59       52       60                                                6 months  53       36       55                                        ______________________________________                                    

In Example 6 and Comparative Example 7, the film was allowed to standoutdoors. In Comparative Example 8, the film was allowed to stand in thedark. Molecular weight was measured by GPC after 3 months on the films.Results are illustrated in Table 7.

                  TABLE 7                                                         ______________________________________                                                    Example                                                                              Comparative                                                                              Comparative                                                 6      Example 7  Example 8                                       ______________________________________                                        Lactic acid base polymer                                                                    P-4      P-4        P-4                                         Ultraviolet                                                                           Compound  HOB      --       --                                        absorber                                                                              wt %      1.0         0        0                                      or                                                                            light                                                                         stabilizer                                                                    Place             out door out door dark                                      Molecular                                                                             0 day     165000   165000   165000                                    weight  3 months   38000    8500     39000                                    ______________________________________                                    

In Example 7 and Comparative Example 9, the films were allowed to standoutdoors. In Comparative Example 10, the film was allowed to stand inthe dark. Molecular weight was measured by 6PC after 2 months on aportion of the films. Results are illustrated in Table 8.

                  TABLE 8                                                         ______________________________________                                                    Example                                                                              Comparative                                                                              Comparative                                                 7      Example 9  Example 10                                      ______________________________________                                        Lactic acid base polymer                                                                    P-5      P-5        P-5                                         Ultraviolet                                                                           Compound  DHB      --       --                                        absorber                                                                              wt %      1.0        0        0                                       or                                                                            light                                                                         stabilizer                                                                    Place             out door out door dark                                      Molecular                                                                             0 day     99000    99000    99000                                     weight  2 months  96000    39000    95000                                     ______________________________________                                    

Examples 8˜11

Ultraviolet absorbers illustrated in Table 9 were individually added toP-10˜P-13 which were obtained in the preparation examples, and mixedwith a Henschel mixer at room temperature to obtain lactic acid basedresin compositions containing the ultraviolet absorbers. Successively,triacetin was added as a plasticizer to the lactic acid base resincompositions prepared from P-10 and P-11 in an amount illustrated inTable 9, and mixed with a Henschel mixer at 180° C. to obtain lacticacid based resin compositions containing ultraviolet absorbers and theplasticizer.

The lactic acid base resin compositions thus obtained were pelletizedwith a twin screw extruder. The pellets obtained were melt-extruded witha single screw extruder to obtain a film having a thickness of 150 μm.Decomposition of the films obtained were measured by the same method ascarried out in Example 7. However, the films were allowed to stand for amonth in Examples 10˜11. Formulations, extruding temperatures andmolecular weight change are illustrated in Table 9.

                                      TABLE 9                                     __________________________________________________________________________                Example 8                                                                           Example 9                                                                           Example 10                                                                          Example 11                                      __________________________________________________________________________    Lactic acid base polymer                                                                  P-10  P-11  P-12  P-13                                            Ultraviolet                                                                         Compound                                                                            TP    HAL + TP                                                                            TP    TP                                              absorber                                                                            wt %  0.1   0.5 + 0.5                                                                           1.0   1.0                                             or                                                                            light                                                                         stabilizer                                                                    Triacetin                                                                           wt part                                                                              5     5     0     0                                              Extrusion temperature                                                                     180   180   180   160                                             (°C.)                                                                  Place       out door                                                                            out door                                                                            out door                                                                            out door                                        Molecular                                                                           0 day 110000                                                                              100000                                                                              36000 70000                                           weight                                                                              1 months                                                                            --    --    33000 67000                                                 2 months                                                                            101000                                                                               88000                                                                              --    --                                              __________________________________________________________________________

Preparation Example 15˜19 [Preparation of Lactic Acid Base Polymer Film]

Ultraviolet absorbers illustrated in table 10 were respectively added tothe lactic acid base polymers P-5 and P-7, P-9, mixed with a Henschelmixer at room temperature to obtain lactic base polymer compositionscontaining the ultraviolet absorbers.

Successively, triacetin was added to the compositions obtained from P-7and P-8, and the LA-oligomer obtained in Preparation Example 6 was addedto the composition obtained from P-9, respectively as a plasticizer in aproportion illustrated in Table 10. These mixtures obtained were blendwith a plastomill at 150° C. in P-7 and P-8 and at 130° C. in P-9.

Sheets having a thickness of 1 mm were prepared by pressing thesecompositions thus obtained under pressure of 50 kg/cm² at 210° C. inP-6, 150° C. in P-7 and P-8, 130° C. in P-9, and at 100° C. in P-5.Successively, these sheets were individually deeply frozen with liquidnitrogen and crushed with a hammer mill to obtain granules of the lacticacid base polymer composition. These granules were successivelymelt-extruded with a single screw extruder and delivered through a T-dieat the temperature illustrated in Table 10 to obtain lactic acid basepolymer films F-1˜F-5 having a thickness of 110˜120 μm.

Formulations, extruding temperature and thickness of these films areillustrated in Table 10.

                                      TABLE 10                                    __________________________________________________________________________                Preparation                                                                         Comparative                                                                          Comparative                                                                          Comparative                                                                          Comparative                                        Example 15                                                                          Example 16                                                                           Example 17                                                                           Example 18                                                                           Example 19                             __________________________________________________________________________    Lactic acid base polymer                                                                  F-1   F-2    F-3    F-4    F-5                                    film                                                                          Polymer                                                                             Compound                                                                            P-6   P-7    P-8    P-9    P-5                                          wt part                                                                             100    90     90     90    100                                    Triacetin (wt part)                                                                       --     10     10    --     --                                     LA oligomer (wt part)                                                                     --    --     --      10    --                                     Ultraviolet                                                                         Compound                                                                            --    TP     TP     TP     DHB                                    absorber                                                                            wt %   0    0.1    1.0    0.05   1.0                                    or                                                                            light                                                                         stabilizer                                                                    Extrusion temperature                                                                     230   150    150    130    130                                    (°C.)                                                                  Film thickness (μm)                                                                    110   100    120    100    100                                    __________________________________________________________________________

Example 12-16 [Preparation of Degradable Adhesive Film]

The lactic acid base polymer films F-1˜F-5 which were obtained inPreparation Examples 15˜19 were used as substrate films.

Separately, 91 parts by weight of butyl acrylate, 4 parts by weight ofacrylonitrile, 2 parts by weight of methacrylic acid and 3 parts byweight of N-methylolmethacrylamide were emulsion polymerized in anaqueous medium to obtain acrylic base adhesive emulsion having a gelcontent of 87% by weight. An adhesive emulsion formulation was preparedby adding 0.5 part by weight of trimethylolpropane polyglycidyl ether tothe emulsion for 100 parts by weight of the solid in the emulsion andheat-treating the mixture at 60° C. for 24 hours.

The adhesive emulsion formulation was applied to one side of the abovesubstrate films F-1˜F-5 with a reverse roll coater so as to obtain adried thickness of 15 μm and dried at 70° C. for 30 minutes to form anadhesive layer. Adhesive was uniformly coated on the whole surface ofsubstrate films and thus coating properties were good.

The coated films were individually wound into rolls on paper tubes so asto put the adhesive layer inside interposing release paper. Thus,degradable adhesive films F-1˜F-5 were obtained and results of propertyevaluation are illustrated in Table 11.

Adhesive strength of the degradable adhesive films obtained in Examples12˜16 were evaluated by the following method.

Adhesive Strength

An adhesive film was adhered to a mirror stainless steel plate (#800ground) with a laminator under pressure of 1 kg/cm² and allowed to standat 23° C. for 24 hours. Thereafter the film was pealed from thestainless steel at a peeling angle of 180 degrees with a pulling rate of300 mm/min. Peeling stress was measured and the measured value wasconverted to a film width of 25 mm.

The film used for evaluation of adhesive strength was buried in soil ata depth of 20 cm for 12 months. Thereafter a molecular weight retentionrate was measured by the following method. Results are illustrated inTable 11.

Molecular Weight Retention Rate

The substrate film portion of the adhesive film which was buried in soilfor 12 months after use was dissolved in chloroform and measuredmolecular weight (polystyrene converted) by GPC. The difference from themolecular weight immediately before preparation was calculated by thefollowing equation.

    DW=100 W.sub.1 /W.sub.0

where

DW: molecular weight retention rate,

W₀ : molecular weight immediately before preparation,

W₁ : molecular weight after burying in soil for 12 months after use.

Tensile strength at break of the adhesive film HF-2 obtained in Example13 was measured at a pulling rate of 50 cm/min. The tensile strength was4.6 kgf/mm². The adhesive film HF-2 adhered to a mirror stainless steelplate (9 800 ground) with a laminator under pressure of 1 kg/cm² andallowed to stand at 23° C. for 21 days. Thereafter the film was peeledfrom the mirror stainless steel plate by the same peeling procedures asabove. Peeling was favorably carried out with a peeling strength of 2.4kgf/mm², which was sufficiently above the minimum tensile strength whichcan favorably peel the film from the stainless steel plate.

Comparative Example 11

A resin composition containing 100 parts by weight of polyvinyl chloridehaving an average polymerization degree of 1100, 35 parts by weight ofdioctyl phthalate, 2 parts by weight of a complex stabilizer, 0.05 partsby weight of ultraviolet absorber TP and 1 part by weight of a complexfatty acid amide (stearylamide: palmitamide=7:3 by weight) wasmelt-processed with a calender to obtain a plasticized polyvinylchloride film having a thickness of 100 μm.

An adhesive film HF-11 was prepared by carrying out the same proceduresas described in Example 12 except that said flexible polyvinyl chloridefilm was used as a substrate film. Properties of the adhesive film HF-11obtained was evaluated by the same methods as carried out in Example 12.Results are illustrated in Table 11.

The film was buried in soil for 12 months. Thereafter the film wasdissolved in tetrahydrofuran and molecular weight retention rate wasmeasured by GPC as carried out in Example 12. Results are illustrated inTable 11.

                                      TABLE 11                                    __________________________________________________________________________                                           Comparative                                     Example 12                                                                          Example 13                                                                          Example 14                                                                          Example 15                                                                          Example 16                                                                          Example 11                             __________________________________________________________________________    Self-adhesive film                                                                     HF-1  HF-2  HF-3  HF-4  HF-5  HF-11                                  Adhesive strength                                                                      108   104   99    109   103   105                                    (g/25 mm)                                                                     Molecular weight                                                                        16    11   10     *1    *1    98                                    retention rate (%)                                                            __________________________________________________________________________     Note                                                                          *1: Sampling was impossible by marked degradation                        

Example 17

The lactic acid base polymer film F-3 obtained in Preparation Example 17was used for the substrate film of a degradable adhesive film.

Separately, 23 parts by weight of methyl methacrylate, 73 parts byweight of 2-ethylhexyl acrylate, 2 parts by weight of glycidylmethacrylate and 2 parts by weight of methacrylic acid were mixed. Themonomer mixture thus obtained was emulsion polymerized in an aqueousmedium to obtain an aqueous acrylic resin base emulsion adhesive havinga solid content of about 47% weight.

An aqueous acrylic resin base emulsion adhesive formulation was preparedby adding to the above obtained emulsion adhesive 10 parts by weight ofdiethylene glycol monobutyl ether, 0.5 part by weight ofpolyoxyethylenenonylphenyl ether surfactant and 0.5 part by weight oftrimethylolpropane polyglycidyl ether crosslinking agent for 100 partsby weight of the solid in the adhesive.

The formulation obtained above was coated with a roll coater on one sideof the above substrate film and dried at 60° C. to obtain a degradableadhesive film HF-6 having an adhesive layer of 10 μm in thickness.Adhesive was uniformly coated over the whole surface of the substratefilm, and thus coating properties were good.

The adhesive film HF-6 obtained was adhered on the surface of asemiconductor silicon wafer (6 inches in diameter and 600 μm inthickness) having a built-in IC. The back of said semiconductor siliconwafer was ground with a rotary surface grinder DEC 82 H/6 (Trade Mark ofDisco Co.) under a wafer feed rate of 200 mm/min, abrasive grain size of40/60 μm (first) and 20/30 μm (second), cooling water 5 l/min, andabrasion loss of 400 μm (600 μm→200 μm). After grinding, the film wasremoved and the wafer was washed with pure water.

The same procedures as above were repeated and the back of 100semiconductor wafers were ground.

No rupture of the semiconductor silicon wafer was found at all in thegrinding operation. It took about an hour for grinding and workabilitywas good.

Adhesive strength of the above-obtained adhesive film HF-6 to the mirrorsilicon wafer was evaluated by the following method. Molecular weightretention rate was measured by the same method as carried out in Example12.

Results are illustrated in Table 12.

Adhesive Strength

A film specimen having a width of 25 mm was adhered on the surface of amirror silicon wafer with a rubber roller under pressure of 2 kg/cm² andallowed to stand at 23° C. under relative humidity of 50% for aprescribed time. Thereafter adhesive strength was measured with anInstron type universal tester by peeling the film specimen from thesurface of the mirror silicon wafer at 23° C. with a peeling angle of180 degrees under a pulling rate of 30 cm/min.

After testing adhesive strength, the adhesive film was buried in soilfor 12 months. Thereafter molecular weight retention rate of the filmwas measured by the same method as carried out in Example 1. Results areillustrated in Table 12.

Comparative Example 12

An ethylene vinyl acetate copolymer (hereinafter referred to as EVAfilm) and polypropylene film were prepared by T-die extrusion process.Both films were laminated to obtain a two-layer lamination film having athickness of 110 μm. A substrate film was prepared by conducting coronadischarge treatment on the surface of EVA film layer of the laminationfilm. An adhesive film HF-12 was prepared by carrying out the sameprocedures as described in Example 17 except that the above-obtainedsubstrate film was used.

Adhesive strength of the film HF-12 to the surface of mirror siliconwafer and molecular weight retention rate were measured by the methoddescribed in Example 17. Results are illustrated in Table 12.

                  TABLE 12                                                        ______________________________________                                                                 Comparative                                                         Example 17                                                                              Example 12                                           ______________________________________                                        Adhesive film    HF-6        HF-12                                            Adhesive Immediately 63          60                                           strength after                                                                (g/25 mm)                                                                              adhesion                                                                      After 1 day 78          80                                                    After 10 day                                                                              125         120                                          Molecular weight 12          97                                               retention rate (%)                                                            ______________________________________                                    

Example 18

The degradable adhesive film HF-2 obtained in Example 13 was adhered tothe whole roof portion of an automotive body (an overall coated newcar). Said automotive body was allowed to stand outdoors for a month.Thereafter, the adhered film HF-2 was removed from the end of the film.The film could be peeled with ease without transfering the automotivecoating to the adhesive film. The portion of automotive surface wherethe film was peeled off had no residue of the adhesive and maintainedgood gloss. Thus, the coated film was in good condition.

Example 19˜22

Degradable adhesive films were prepared by furnishing an adhesive layeras carried out in Example 12 except that the lactic acid base polymerfilms obtained in Examples 8˜11 were used as substrate films.

Coating properties of the adhesive to these substrate films were good inany cases. The degradable adhesive films obtained were individuallyadhered on mirror stainless steel plates and allowed to stand at 23° C.for a week. Thereafter these films could be favorably peeled from thestainless steel plates. The degradable adhesive film thus peeled wereburied in soil and extremely degraded after 12 months.

Example 23˜27

The lactic acid base polymer films F-1˜F-5 obtained in PreparationExamples 15˜19 were printed on one surface with an offset printingmachine, Model RI-1 (Trade Mark of Mei Seisakusho Co.) by using an inkBEST-ONE-PROCESS-BLACK-H (Trade Mark of Touka Dystuff Chemical IndustryCo.). The printed films were naturally dried by allowing to stand atroom temperature under 40% relative humidity for 3 days. Printed statewas good. Ink transfer amount estimated by transmission density was1.3˜2.9 g/m², which was almost the same as the transfer amount of aMylar base photograying transparent film.

Separately, 91 parts by weight of butyl acrylate, 4 parts by weight ofacrylonitrile, 2 parts by weight of methacrylic acid and 3 parts byweight of N-methylolmethacrylamide were emulsion polymerized in anaqueous medium to obtain an acrylic base adhesive emulsion having a gelcontent of 87% by weight. An adhesive emulsion formulation was preparedby adding 2 parts by weight of trimethylolpropane polyglycidyl ether tothe adhesive emulsion for 100 parts by weight of the solid in theemulsion and heat-treating at 60° C. for 24 hours.

The adhesive emulsion formulation was coated on the back (the other sideof the printed surface) of the above printed films with a reverse rollcoater so as to obtained a dried thickness of 15 μm and dried at 70° C.for 30 minutes to install an adhesive layer. Thus, degradable adhesiveindication films PF-1˜PF-5 were obtained. The adhesive was uniformlycoated over the whole surface of the substrate film and coatingproperties were good.

The degradable adhesive indication films PF-1˜PF-5 thus obtained wereindividually wound into rolls on paper tubes so as to put the adhesivelayer inside while interposing a release film. Ink transfer amount ofPF-1˜PF-5 was measured by the following method. Molecular weightretention rate was measured by the same method as described in Example12. Results are illustrated in Table 13.

Ink Transfer Amount

Transmission density of a printed film was measured with a Macbeth ModelTD-903 transmission densitometer. The ink transfer amount was estimatedby comparing the measured density with transmission density of a filmhaving a known amount of ink.

Comparative Example 13

A resin composition containing 100 parts by weight of a polyvinylchloride having an average polymerization degree of 1100, 35 parts byweight of dioctyl phthalate, 2 parts by weight of a complex stabilizer,0.05 part by weight of an ultraviolet absorber, BIOSORB-130 (Trade Markof Kyodo Yakuhin Co.) and 1 part by weight of complex fatty acid amide(Stearyl amide: palmitamide=7:3 by weight) was melt-kneaded and rolledwith a calender to obtain a plasticized polyvinyl chloride film having athickness of 1110 μm.

A degradable adhesive indication film PF-R was prepared by carrying outthe same methods of printing and adhesive coating as described inExample 23 except that the flexible polyvinyl chloride film obtainedabove was used as a substrate film. Properties of PF-R obtained wereevaluated by the same method as described in Example 23 and results areillustrated in Table 13. The film was buried in soil for 12 months andthen dissolved in tetrahydrofuran and molecular weight retention ratewas measured by GPC as carried out in Example 23. Results areillustrated in Table 13.

                                      TABLE 13                                    __________________________________________________________________________                                            Comparative                                     Example 23                                                                          Example 24                                                                          Example 25                                                                          Example 26                                                                          Example 27                                                                          Example 13                            __________________________________________________________________________    Self-adhesive film                                                                      PF-1  PF-2  PF-3  PF-4  PF-5  PF-R                                  Substrate film                                                                          F-1   F-2   F-3   F-4   F-5   Plasticized                                                                   PVC film                              Ink transfer amount                                                                     2.9   1.3   1.7   2.6   2.3   2.5                                   (g/m.sup.2)                                                                   Printed state                                                                           good  good  good  good  good  good                                  Adhesive Strength                                                                       115   111   103   106   108   109                                   (g/25 mm)                                                                     Molecular weight                                                                         19    18    8     *1    *1    94                                   retention rate (%)                                                            __________________________________________________________________________     Note                                                                          *1: Sampling was impossible by marked degradation                        

Examples 28˜31

Offset printing was carried out by the same procedures as described inExample 23 except that the lactic acid base polymer films obtained inExamples 8˜11 were used as substrate films. Successively, the adhesivelayer was installed on these printed films to obtain degradable adhesiveindication films. Adhesive was uniformly coated over the whole surfaceof the substrate films and thus coating properties were good.

Ink transfer amount of these degradable adhesive indication films wasmeasured by the same method as described in Example 23. Ink transferamount was in the range of 1.6˜2.8 g/m².

Examples 32˜33

Rotogravure printing was carried out on one side of the lactic acid basepolymer films F-1 and F-2 which were obtained in Preparation Example 15and 16, respectively, with a baby type gravure printing machine by usinga 35 μm solid plate for coating. Two component type ink for polyethyleneterephthalate (PET) was used in Example 32. Single component type inkfor polystyrene was used in Example 33. After printing, the printedsurface was dried with a household hair dryer. Printability and adhesiveproperties of ink were evaluated by the following methods. Results weregood and are illustrated in Table 14.

The adhesive emulsion formulation was coated on the other side (the backof printed surface) of the printed films so as to obtain dried thicknessof 15 μm by carrying out the same procedures as described in Example 23and dried to install an adhesive layer. Thus, degradable adhesiveindication films PF-6˜PF-7 were obtained.

Adhesive strength and molecular weight retention rate after 12 months ofPF-6˜PF-7 were measured by the same methods as described in Example 23.Results are illustrated in Table 14.

Printability

A printed film sample was visually observed.

Printability was regarded as good when the printed ink had uniformdensity and lifting of ink, stripe or band unevenness of printing werenot found on the surface.

Ink Adhesion

A cellophane tape NICHIBAN (Trade Mark of Nichiban Co.) having a widthof 25 mm was adhered on the printed surface of dried film sample at theroom temperature by pressing with fingers and immediately peeled off.

Adhesive properties were regarded as good when the printed ink was notpeeled from the surface film.

                  TABLE 14                                                        ______________________________________                                                      Example 32                                                                            Example 33                                              ______________________________________                                        Adhesive film   PF-6      PF-2                                                Substrate film  F-1       F-2                                                 Ink             for PET   for polystyrene                                     Printability    good      good                                                Ink adhesion    good      good                                                Adhesive Strength                                                                             103       112                                                 (g/25 mm)                                                                     Molecular weight                                                                               21        16                                                 retention rate (%)                                                            ______________________________________                                    

The present invention may be practiced or embodied in still other wayswithout departing from the spirit or essential character thereof.

However, these examples are not intended to limit the scope of thepresent invention and the invention may be practiced or embodied instill other ways without departing from the spirit or essentialcharacter thereof.

We claim:
 1. A degradable adhesive film comprising a substrate filmobtained from a lactic acid base polymer and an adhesive layer on oneside of the substrate film, wherein the substrate film comprises 0.001˜5parts by weight of at least one additive selected from the groupconsisting of an ultraviolet absorber and a light stabilizer for 100parts by weight of the lactic acid base polymer, and the adhesive layercomprises an adhesive and 0.01˜20 parts by weight of a crosslinkingagent selected from the group consisting of epoxy based resins, melaminebased resins and aziridine based resins for 100 parts by weight of theadhesive.
 2. A degradable adhesive film of claim 1 wherein the lacticacid base polymer is one or more polymers selected from the groupconsisting of polylactic acid and a lactic acid/hydroxycarboxylic acidcopolymer.
 3. A degradable adhesive film of claim 1 wherein the lacticacid base polymer has a molecular weight of 30,000˜500,000.
 4. Adegradable adhesive film of claim 2 wherein the polylactic acid is oneor more polymers selected from the group consisting of poly(L-lacticacid) or poly(DL-lactic acid) having 50˜100% by mole of L-lactic acidunits and poly(D-lactic acid) or poly(DL-lactic acid) having 50˜100% bymole of D-lactic acid units.
 5. A degradable adhesive film of claim 2wherein the lactic acid/hydroxycarboxylic acid copolymer is one or morepolymers selected from the group consisting of a lactic acid/glycolicacid copolymer having 30˜98% by mole of lactic acid units and 70˜2% bymole of glycolic acid units, and a lactic acid/hydroxycaproic acidcopolymer having 10˜98% by mole of lactic acid units and 90˜2% by moleof hydroxycaproic acid units.
 6. A degradable adhesive film of claim 1wherein the substrate film comprises 1˜50 parts by weight of one or moreplasticizers selected from the group consisting of glycerol triacetate,lactic acid, a lactic acid oligomer having polymerization degree of2˜10, and lactide for 100 parts by weight of the lactic acid basepolymer. weight of the lactic acid base polymer.
 7. A degradableadhesive film of claim 1 wherein the additives are one or more compoundsselected from the group consisting of benzophenones including2-hydroxy-4-n-octoxybenzophenone and 4-dodecyloxy-2-hydroxybenzophenone,benzotriazoles including 2-(2'-hydroxy-5'-methylphenyl)benzotriazole and2-(2'-hydroxy-3',5'-di-tert-butylphenyl)benzotriazole, and sebacatesincluding bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate.
 8. A degradableadhesive film of claim 1 wherein the adhesive is one or more compoundsselected from the group consisting of a natural rubber based adhesive, asynthetic rubber based adhesive and a synthetic resin based adhesive. 9.A degradable adhesive film of claim 8 wherein the synthetic resin basedadhesive is an acrylic resin based adhesive.
 10. A degradable adhesivefilm of claim 9 wherein the acrylic resin is a copolymer comprising anacrylic acid alkyl ester and a monomer having a carboxyl group.
 11. Adegradable adhesive film of claim 1 wherein one or both sides ofsubstrate film are printed or painted.